1. Field of the Invention
The present invention relates to a tank cap having a torque mechanism to close a tank opening by a predetermined rotational torque and a fuel tank with the tank cap attached thereto.
2. Description of Related Art
A known tank caps attached to a fuel tank of an automobile is disclosed in Japanese Patent Publication Gazette No. 6-88606. FIG. 36 is a sectional view illustrating a prior art tank cap 300. The tank cap 300 includes a plastic casing main body 302 that is screwed to a fuel supply inlet FNb of a fuel tank (not shown), a cover 330 that is attached to the casing main body 302, and a negative pressure valve 340 that is accommodated in a valve chest 304 formed in the casing main body 302 and regulates the pressure in the fuel tank. The negative pressure valve 340 includes a rubber valve disk 342, a valve support member 346 that has an opening 346a into which the valve disk 342 is fit, and a spring 348 that presses the valve disk 342. When the differential pressure between the tank pressure and the atmospheric pressure applied to the valve disk 342 exceeds a predetermined level, the valve disk 342 is set in an open position against the pressing force of the spring 348 in order to make the tank pressure closer to the atmospheric pressure.
A torque mechanism 320 is disposed between the upper portion of the casing main body 302 and the cover 330. While the casing main body 302 is attached to the fuel supply inlet FNb of the fuel tank, when the rotational torque applied to the cover 330 in the closing direction of the fuel supply inlet FNb exceeds a predetermined level, the torque mechanism 320 raises the cover 330 relative to the casing main body 302. This arrangement prevents the fuel supply inlet FNb from being closed with an excessively large force applied to the tank cap 300.
In the prior art structure discussed above, since many rotations of the tank cap are required to close the fuel supply inlet, this is rather troublesome. A proposed torque mechanism to solve this problem is capable of making the tank cap close the fuel supply inlet by a rotation of approximately 90 degrees. In the proposed technique, however, the positional relationship between the cover and the casing main body is gradually shifted in the rotating direction. A rather complicated operation is required for user to position the tank cap in the fuel supply inlet. This results in the poor operability of the tank cap.